Optimizing the Definition of Ischemic Core in CT Perfusion: Influence of Infarct Growth and Tissue-Specific Thresholds

Abstract

BACKGROUND AND PURPOSE: CTP allows estimating ischemic core in patients with acute stroke. However, these estimations have limited accuracy compared with MR imaging. We studied the effect of applying WM-and GM-specific thresholds and analyzed the infarct growth from baseline imaging to reperfusion. MATERIALS AND METHODS:This was a single-center cohort of consecutive patients (n ¼ 113) with witnessed strokes due to proximal carotid territory occlusions with baseline CT perfusion, complete reperfusion, and follow-up DWI. We segmented GM and WM, coregistered CTP with DWI, and compared the accuracy of the different predictions for each voxel on DWI through receiver operating characteristic analysis. We assessed the yield of different relative CBF thresholds to predict the final infarct volume and an estimated infarct growth-corrected volume (subtracting the infarct growth from baseline imaging to complete reperfusion) for a single relative CBF threshold and GM-and WM-specific thresholds. RESULTS:The fixed threshold underestimated lesions in GM and overestimated them in WM. Double GM-and WM-specific thresholds of relative CBF were superior to fixed thresholds in predicting infarcted voxels. The closest estimations of the infarct on DWI were based on a relative CBF of 25% for a single threshold, 35% for GM, and 20% for WM, and they decreased when correcting for infarct growth: 20% for a single threshold, 25% for GM, and 15% for WM. The combination of 25% for GM and 15% for WM yielded the best prediction.CONCLUSIONS: GM-and WM-specific thresholds result in different estimations of ischemic core in CTP and increase the global accuracy. More restrictive thresholds better estimate the actual extent of the infarcted tissue.ABBREVIATIONS: ICC ¼ intraclass correlation coefficient; IG ¼ infarct growth; IQR ¼ interquartile range; rCBF ¼ relative CBF C TP is a widely available technique that allows measuring hypoperfused brain tissue and estimating ischemic core in patients with acute stroke. [1][2][3] The ischemic core is often defined by CBF thresholds. 4 However, despite their clinical usefulness, the most often used CBF-based definitions of ischemic core may not be accurate for research purposes. 5 They often overestimate the true infarct 6 (example in the Online Supplemental Data) and have limited accuracy compared with MR imaging. 7 In addition, differences in the neurochemical response to ischemia in GM and WM lead to a varied vulnerability to ischemia. 8 Applying homogeneous CBF thresholds in the whole brain may result in under-or overestimating the lesion in brain areas with different susceptibility to ischemia. 9 Also, ischemic core volumes estimated by CTP, especially those affecting WM, are often smaller than in follow-up MR imaging. 10 This overestimation, applied to routine clinical practice, could lead to not offering reperfusion treatment to patients who could benefit from it. These findings can be explained by the delay between baseline imaging and the followup imaging used to measure final infarct volume. The b...

Ghost infarct core: A systematic review of the frequency, magnitude, and variables of CT perfusion overestimation

“…Applying more stringent imaging thresholds, such as CBF < 20% or 25%, was associated with significantly lower rates of core overestimation 19,26 . Similarly, applying different CBF thresholds to account for the differential ischemic vulnerability between gray and white matter has been shown to minimize overestimation 19,27–31 . A limitation of these studies is that complete recanalization (TICI 3) was not a requirement in all studies and some studies had long CTP to reperfusion times, which may have diluted the degree of overestimation.…”

“…19,26 Similarly, applying different CBF thresholds to account for the differential ischemic vulnerability between gray and white matter has been shown to minimize overestimation. 19,[27][28][29][30][31] A limitation of these studies is that complete recanalization (TICI 3) was not a requirement in all and some studies had long CTP to reperfusion times, which may have diluted the degree of overestimation. Furthermore, mechanical thrombectomy was not performed in consecutive patients in any of these studies but was performed at the discretion of the provider.…”

CT perfusion extended window ischemic core estimation: Bayesian algorithm versus oscillation index singular value decomposition

“…17 Several studies have compared CTp ischemic core with DWI performed several days later. [18][19][20][21] Unfortunately, even follow-up imaging provides an imperfect core measurement. 22 Only 24 of 148 stroke patients in the extended window were studied with both CTp and DWI.…”

“…Several studies have compared CTp ischemic core with DWI performed several days later 18–21 . Unfortunately, even follow‐up imaging provides an imperfect core measurement 22 …”

Out of the core: the impact of focal ischemia in regions beyond the penumbra

“…The core may be defined as a region with a decrease of regional blood flow below 35 % in the grey matter and below 25 % in the white matter (WM) in human brain ( Rodriguez-Vazquez et al, 2022 ). Hartings et al (2017) claim the core can be best described as an area of persistent depolarization with the regional blood flow failing to reach 5 – 10 ml/100 g/min ( Hartings et al, 2017 ).…”